Finding torque in xyz coordinates

  • #1
Problem:
An engineer estimates that under the most adverse expected weather conditions, the total force on the highway sign in the figure below will be F = 2.48i - 2.88j kN, acting at the center of mass (CM).

Assume that L1 = 8.13 m and L2 = 6.45 m. What are the x, y, z components of the torque that this force exerts about the base O? Enter components in the order x, y, z.

i knoe that i have to use the formula T = r X F

and F = 2.48i - 2.88j + 0k

i set r = 0i + 8.13j + 6.45k

and using cross product i got T = 18.576i - 15.996j - 20.1624k N*m

the answer is still wrong.... what am i doing wrong?
 

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Answers and Replies

  • #2
dav2008
Gold Member
609
1
Without checking any of the work specifically, make sure to account for the fact that the force is given in kiloNewtons, not Newtons.

As far as your cross product, I think you have a sign reversed.
 

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